Catastrophic health expenditure in sub-Saharan Africa: systematic review and meta-analysis

Abstract Objective To estimate the incidence of, and trends in, catastrophic health expenditure in sub-Saharan Africa. Methods We systematically reviewed the scientific and grey literature to identify population-based studies on catastrophic health expenditure in sub-Saharan Africa published between 2000 and 2021. We performed a meta-analysis using two definitions of catastrophic health expenditure: 10% of total household expenditure and 40% of household non-food expenditure. The results of individual studies were pooled by pairwise meta-analysis using the random-effects model. Findings We identified 111 publications covering a total of 1 040 620 households across 31 sub-Saharan African countries. Overall, the pooled annual incidence of catastrophic health expenditure was 16.5% (95% confidence interval, CI: 12.9–20.4; 50 datapoints; 462 151 households; I2 = 99.9%) for a threshold of 10% of total household expenditure and 8.7% (95% CI: 7.2–10.3; 84 datapoints; 795 355 households; I2 = 99.8%) for a threshold of 40% of household non-food expenditure. Countries in central and southern sub-Saharan Africa had the highest and lowest incidence, respectively. A trend analysis found that, after initially declining in the 2000s, the incidence of catastrophic health expenditure in sub-Saharan Africa increased between 2010 and 2020. The incidence among people affected by specific diseases, such as noncommunicable diseases, HIV/AIDS and tuberculosis, was generally higher. Conclusion Although data on catastrophic health expenditure for some countries were sparse, the data available suggest that a non-negligible share of households in sub-Saharan Africa experienced catastrophic expenditure when accessing health-care services. Stronger financial protection measures are needed.


Introduction
In 2019, over 930 million people worldwide experienced financial hardship while obtaining health care and, annually, about 100 million people were impoverished. 1 Out-of-pocket payments, the predominant form of health care financing in sub-Saharan Africa, have hindered the region's drive towards universal health coverage (UHC) and attainment of the sustainable development goals (SDGs). [2][3][4] Moreover, payments affect the poorest households disproportionately, thereby exacerbating inequality. 3,5 Catastrophic health expenditure has been defined as out-of-pocket payments above a share of total household expenditure or non-food expenditure that forces households to sacrifice other basic needs, sell assets, incur debts or become impoverished. 6,7 This perpetuates a vicious cycle of poverty for poor households and leads to more illness when households cannot afford out-of-pocket costs. 2,8 Reducing the incidence of catastrophic health expenditure is a key policy objective of governments in sub-Saharan Africa. 2 However, the design and implementation of appropriate policies requires accurate, up-to-date evidence on the incidence of catastrophic health expenditure, which is scant at present.
Our aim was to fill this evidence gap by performing a systematic review of population-based studies of catastrophic health expenditure in sub-Saharan Africa. In particular, we aimed to estimate the magnitude of, and between-country variation in, the annual incidence of catastrophic health expenditure between 2000 and 2021 and to investigate trends over time.

Methods
We searched the PubMed®, African Journals Online, CINAHL, CNKI, African Index Medicus, PsycINFO, SciELO, Scopus and Web of Science databases using terms covering catastrophic health expenditure, financial catastrophe and sub-Saharan Africa (Box 1; available at: https:// www .who .int/ publications/ journals/ bulletin/ ) for studies published between 1 January 2000 and 30 September 2021 in the 48 countries of sub-Saharan Africa (Box 2), as defined by the World Bank. 9 In addition, two authors independently searched the published literature between 2 October and 10 October 2021. We also searched the New York Academy of Medicine Grey Literature and Open Grey, two prepublication server depositories (i.e. medRxIV and bioRxIV) and Google Scholar ® for grey literature and followed up citations in studies identified through the database search. We considered studies published in any of the six African Union languages: Arabic, English, French, Kiswahili, Portuguese and Spanish. Studies not in English were translated. The two authors underwent a moderation exercise to ensure that inclusion and exclusion criteria (Box 3) were applied uniformly before independently assessing titles and abstracts. Discrepancies were resolved by discussion. Finally, the full texts of eligible articles were assessed against the inclusion criteria. We registered the study protocol on PROSPERO (CRD42021274830) and findings were reported according to PRISMA guidelines. 11 Three authors independently extracted data from the included studies on: (i) study countries; (ii) year of publication; (iii) study design; (iv) data sources; (v) year of data collection; Objective To estimate the incidence of, and trends in, catastrophic health expenditure in sub-Saharan Africa. Methods We systematically reviewed the scientific and grey literature to identify population-based studies on catastrophic health expenditure in sub-Saharan Africa published between 2000 and 2021. We performed a meta-analysis using two definitions of catastrophic health expenditure: 10% of total household expenditure and 40% of household non-food expenditure. The results of individual studies were pooled by pairwise meta-analysis using the random-effects model. Findings We identified 111 publications covering a total of 1 040 620 households across 31 sub-Saharan African countries. Overall, the pooled annual incidence of catastrophic health expenditure was 16.5% (95% confidence interval, CI: 12.9-20.4; 50 datapoints; 462 151 households; I 2 = 99.9%) for a threshold of 10% of total household expenditure and 8.7% (95% CI: 7.2-10.3; 84 datapoints; 795 355 households; I 2 = 99.8%) for a threshold of 40% of household non-food expenditure. Countries in central and southern sub-Saharan Africa had the highest and lowest incidence, respectively. A trend analysis found that, after initially declining in the 2000s, the incidence of catastrophic health expenditure in sub-Saharan Africa increased between 2010 and 2020. The incidence among people affected by specific diseases, such as noncommunicable diseases, HIV/AIDS and tuberculosis, was generally higher. Conclusion Although data on catastrophic health expenditure for some countries were sparse, the data available suggest that a nonnegligible share of households in sub-Saharan Africa experienced catastrophic expenditure when accessing health-care services. Stronger financial protection measures are needed.
(vi) study population; (vii) sample size; and (viii) the incidence of catastrophic health expenditure as determined using a threshold of 10% of total household expenditure or 40% of household nonfood expenditure or both. For surveys spanning several years, we regarded the survey's first year as the date of the survey. We grouped countries into four regions (i.e. central, eastern, southern and western Africa) using the African Union classification (Box 2) and into three income categories (i.e. low, lower middle and upper middle) using the World Bank's classification. 9, 10 We obtained data on social health insurance programme coverage as a percentage of the country's population from the World Bank and on the UHC's service coverage index from the World Health Organization's (WHO) Global Health Expenditure Database. 12,13 The service coverage index for 2015 was used for studies whose data were collected before 2016, whereas the index for 2017 was used for all other studies. 13 Although studies have used different thresholds to define catastrophic health expenditure, 6,14 the two most widely used are 10% of total household expenditure and 40% of household nonfood expenditure. 15,16 We estimated the annual incidence of catastrophic expenditure from the studies included using these thresholds. If catastrophic expenditure was not reported using either of these two definitions, we contacted the study's authors for supplementary information. We included catastrophic expenditure estimates based on the medical expenditure incurred only; 14 estimates based on indirect costs, such as transportation, were excluded. We contacted study authors if estimates were missing or reported only monthly or weekly. If two or more studies used the same secondary data to estimate the incidence of catastrophic health expenditure, we used estimates from peer-reviewed studies and from studies that reported catastrophic health expenditure using both definitions.
Three authors independently assessed study quality using the appraisal tool for cross-sectional studies (AXIS) -a 20-question checklist designed to assess a study's risk of bias across five domains: introduction, methods, results, discussion and other information. 17 Each study was scored between 0 and 20, with a high score indicating a low risk of bias. Discrepancies between authors were resolved by discussion.

Data analysis
We used descriptive statistics to summarize the studies' characteristics. Individual results were pooled by pairwise meta-analysis using the random-effects model (DerSimonian-Laird approach) and the MetaProp Stata command with the Freeman-Tukey double arcsine transformation. 18 We conducted separate meta-analyses for the two definitions of catastrophic health expenditure. Between-study heterogeneity was assessed using the χ 2 test with Cochran's Q statistic and quantified using the I 2 statistic. We used Stata v. 17.0 (StataCorp LLC, College Station, United States of America) for all statistical analyses and an α of 0.05 was the cut-off for statistical significance.
We assessed the sensitivity of the pooled estimates to sample size by excluding the 10% of studies with the smallest sample size and the 10% with the largest sample size. The robustness of the estimates was assessed by excluding: (i) studies with the largest and smallest sample sizes; (ii) studies using

Inclusion criteria
• Observational or interventional studies (which included data on the pre-intervention period) published between 2000 and 2021 that reported population-level data for any of the 48 sub-Saharan African countries defined by the World Bank (Box 2). 9 • Studies reported in the published or unpublished (i.e. grey) literature. • Publications that reported the incidence of catastrophic health expenditure for all individuals of all ages in the community as identified through household surveys or through studies based in health facilities that were representative of the entire community. • Peer-reviewed publications in Arabic, English, French, Portuguese, Spanish or Kiswahili. • Publications that estimated catastrophic health expenditure using either total household expenditure or income or non-subsistence expenditure. • Publications that reported data on catastrophic health expenditure that could be extracted as an independent outcome along with the study population (i.e. the denominator).

Exclusion criteria
• Publications that reported the incidence or proportion of catastrophic health expenditure based on a retrospective analysis of patients' charts, an analysis of hospital or pharmacy revenues, or a national or subnational budget analysis. • Publications that reported the incidence of catastrophic health expenditure for all individuals of all ages based on studies carried out in one or several health facilities (e.g. outpatient clinics, hospitals with inpatients, intensive care units, operating theatres, nursing homes or long-term care facilities) that were not representative of the entire community. • Interventional studies that reported the incidence of catastrophic health expenditure only after the intervention. • Studies that used methods for estimating catastrophic health expenditure that were not clearly reported or defined or that reported catastrophic expenditure using terms such as "excessive out-of-pocket health care" or the multidimensional poverty index. • Articles that reported data for a population already included in the systematic review. • Case reports, case series, systematic reviews, narrative reviews, letters to editors, commentary pieces and study protocols. (iv) data type (i.e. primary or secondary); (v) publication status (i.e. peer-reviewed or not); (vi) UHC service coverage index (dichotomized to < 45 and ≥ 45, based on the sub-Saharan African average reported by WHO); 13 (vii) the proportion of households with social insurance (i.e. < 10% or ≥ 10%); and (viii) the studies' risk of bias (i.e. high or low, corresponding to an AXIS score of 0-10 or 11-20, respectively).
Finally, we performed a meta-regression analysis to explore factors associated with between-study heterogeneity for all catastrophic health expenditure incidence estimates pooled from 10 or more datapoints. 19 To avoid overfitting the model, we included a limited number of covariates (selected on the basis of   15,16 and (ii) country-level factors, namely income status, UHC service coverage index and the proportion of the population with social insurance. 2,4,7 We also evaluated evidence of publication bias by examining funnel plot symmetry; we performed Egger's test for small-study effects and used the trim-and-fill method. 19 We assessed overall evidence quality using the Grading of Recommendations, Assessment, Development and Evaluation (GRADE) approach. 20 First, we scored the evidence for each outcome as high and downgraded it by one level if one of the following was present: (i) poor methodological quality (i.e. if 25% or more of the studies in the meta-analysis had a high risk of bias); (ii) imprecision (i.e. if 25% or more of the studies did not have a sample size of at least 385 households -the smallest sample size at the 95% confidence interval [CI] and 5% error margin); (iii) indirectness (i.e. if 25% The threshold for catastrophic health expenditure was defined as 10% of total household expenditure. b Countries in sub-Saharan Africa were grouped into four regions using the African Union classification. 10 c Countries' income status was classified as low, lower middle or upper middle using the World Bank's classification. 9 d Study quality was assessed using the appraisal tool for cross-sectional studies (AXIS) score: 17 an AXIS score of 0-10 indicated a high risk of bias and a score of 11-20 indicated a low risk.

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Catastrophic health expenditure, sub-Saharan Africa Paul Eze et al.
or more of the studies did not use valid and reliable methods of data collection, such as validated questionnaires that had been trialled, piloted or published previously); and (iv) inconsistency (i.e. if the prediction interval for the outcome had a variation of 10% or more between the upper and lower limits of the 95% CI). These criteria were based on Joanna Briggs guidelines, which correspond to the GRADE system criteria. 21

Results
Our initial search identified 1623 studies, including 36 from Google Scholar and citation tracking (Fig. 1). After removing duplicates, 1365 titles and abstracts were screened. Of the 159 articles whose full text was assessed, 111 finally met the inclusion criteria ( The studies covered a total of 1 040 620 households across 31 countries in sub-Saharan Africa (Fig. 2) and reported 145 distinct datapoints: 50 derived from primary data and 95 derived from secondary data. Each datapoint represented a value for the annual incidence of catastrophic health expenditure in a specific country in a specific year. Of the 145 datapoints, 6, 53, 32 and 54 related to central, eastern, southern and western Africa, respectively. The countries with the most datapoints were Nigeria (20), Kenya (14), South Africa (12) and Ghana and Ethiopia (11 each The quality of 95 of the 111 included studies (85.6%) was rated as high (AXIS score: [11][12][13][14][15][16][17][18][19][20], whereas the quality of the remaining 16 (14.4%) was rated as low (AXIS score: 0-10). When the risk of bias was weighted accord-ing to each study's sample size, studies covering 88.6% (921 704/1 040 620) of households included were rated as having a low risk of bias, whereas those covering 11.4% (118 916/1 040 620) were judged to have some quality concerns or were rated as having a high risk of bias. Of note, all studies included used sample frames and sampling techniques that closely represented the underlying population (as assessed using AXIS tool items 5 and 6).

Household expenditure threshold
When the threshold for catastrophic health expenditure was defined as 10% of total household expenditure, the pooled annual incidence across 50 datapoints, which covered 462 151 households, was 16.5% (95% CI: 12.9-20.4; Table 2). Further details are available in the data repository. 133 In the sensitivity analyses, excluding the 10% of studies with the smallest sample sizes yielded a slightly lower pooled incidence of 15.0% (95% CI: 11.4-19.0; 45 datapoints; 459 989 households), whereas excluding the 10% of studies with the largest sample sizes yielded a slightly higher pooled incidence of 17.8% (95% CI: 13.8-22.3; 45 datapoints; 317 634 households). The difference was not great.
When poor-quality studies were excluded, the estimated pooled incidence was 15.4% (95% CI: 12. At the country level, Cameroon and Sudan had the highest and second highest incidence, at 65.0% (95% CI: 64.1-65.9) and 52.8% (95% CI: 52.1-53.5), respectively (details available in the data repository). 133 Regionally, the pooled incidence for countries in central and western Africa was higher than that for the whole of sub-Saharan Africa ( Table 2). The incidence was highest for countries in central Africa, at 50.6% (95% CI: 49.8-51.4; two datapoints; 14 423 households), and lowest for countries in southern Africa, at 8.4% (95% CI: 6.0-11.1; 10 datapoints; 132 085 households). Univariate meta-regression analysis indicated that the between-study variation in the pooled incidence was associated with: (i) study quality as assessed using the AXIS score (P-value 0.005); (ii) the country's income status (P-value 0.005); and (iii) the country's UHC service coverage index (P-value 0.005). Full details are available in the data repository. 133 However, multivariable meta-regression analysis indicated that no variable was independently associated with betweenstudy differences in the estimated pooled incidence.

Non-food expenditure threshold
When the threshold for catastrophic health expenditure was defined as 40% of household non-food expenditure, the pooled annual incidence across 84 datapoints, which covered 795 355 households, was 8.7% (95% CI: 7.2-10.3; Table 3). Further details are

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Catastrophic health expenditure, sub-Saharan Africa Paul Eze et al.
available in the data repository. 133 In the sensitivity analyses, excluding the 10% of studies with the smallest sample sizes yielded a slightly lower pooled incidence of 7.9% (95% CI: 6.5-9.5; 75 datapoints; 789 746 households), whereas excluding the 10% of studies with the largest sample sizes yielded a slightly higher pooled incidence of 9.3% (95% CI: 7.5-11.3; 75 datapoints; 480 710 households). The incidence estimates were similar. When poorquality studies were excluded, the pooled incidence was slightly lower at 7.9% (95% CI: 6.4-9.5; 73 datapoints; 691 778 households). Between 2000 and 2019, the pooled incidence initially decreased but increased between 2010-2014 and 2015-2019 ( Fig. 3). At the country level, the Democratic Republic of the Congo and Mali had the highest and second highest incidence, at 21.9% (95% CI: 20.5-23.4) and 19.1% (95% CI: 18.1-20.2), respectively Countries in sub-Saharan Africa were grouped into four regions using the African Union classification. 10 c Countries' income status was classified as low, lower middle or upper middle using the World Bank's classification. 9 d Study quality was assessed using the appraisal tool for cross-sectional studies (AXIS) score: 17 an AXIS score of 0-10 indicated a high risk of bias and a score of 11-20 indicated a low risk.

Systematic reviews
Catastrophic health expenditure, sub-Saharan Africa Paul Eze et al.
(details in the data repository). 133 Regionally, the estimated pooled incidence for countries in central, eastern and western Africa were all higher than the pooled incidence for the whole of sub-Saharan Africa ( Table 3). The pooled incidence for lower-middle-income countries was higher, at 10.8% (95% CI: 8.8-13.0; 48 datapoints; 487 490 households), than for low-income countries, at 7.6% (95% CI: 4.8-11.1; 23 datapoints; 182 466 households). Univariate meta-regression analysis indicated that the between-study variation in pooled incidence was associated with: (i) whether primary or secondary data had been used (P-value < 0.001); (ii) study quality as assessed using the AXIS score (P-value < 0.001); (iii) the country's income status (P-value 0.001); and (iv) the country's UHC service coverage index (P-value 0.001). Full details are available in the data repository. 133 However, multivariable meta-regression analysis indicated that only study data type (P-value 0.024) and study quality (P-value 0.009) were independently associated with between-study differences in estimated pooled incidence. On average, studies that used secondary data reported a lower incidence of catastrophic health expenditure than those using primary data.

Disease-specific catastrophic expenditure
Estimates of the pooled incidence of catastrophic health expenditure for different disease groups (Table 4) were generally higher than estimates for the whole population (Table 2 and Table 3).

Publication bias
For the population-level meta-analyses, visual inspection of funnel plots suggested there was no publication bias. However, Egger's test for small-study effects gave a significant result (P-value 0.003 when the threshold was 10% of total household expenditure and P-value < 0.001 when it was 40% of household non-food expenditure). We were unable to determine whether the small-study effect was driven by publication bias because there was substantial heterogeneity in the data. For both thresholds, trim-andfill analysis suggested that publication bias was absent (details available in the data repository). 133 Similar assessments performed for the disease-specific metaanalyses also suggested that publication bias was absent.

Evidence quality
The quality of the evidence used for estimating the incidence of catastrophic health expenditure at the population level with both thresholds was graded as high as there was no serious risk of bias, imprecision, indirectness or inconsistency (Table 5) . However, the quality of the evidence used for estimating the incidence of disease-specific catastrophic expenditure varied from low to high because, for some disease groups, there was serious imprecision, a serious risk of bias and serious inconsistency across the studies.

Discussion
Our findings suggest that one in six households in sub-Saharan Africa experienced a financial catastrophe when seeking health care between 2000 and 2019. Our review also indicates that the incidence of catastrophic health expenditure increased between 2010-2014 and 2015-2019. This increase could be due to the higher cost of health care, of both medications and medical consultations. 15,134,135 The result is financial difficulty for households, and exerts fiscal pressure on the strained health budget of many countries. 134 Over the last two decades, rapid population growth, ageing, urbanization and a sedentary lifestyle have increased the incidence of noncommunicable diseases in sub-Saharan Africa. 136 Catastrophic health expenditure is unlikely to fall in the near future unless drastic measures are taken to counter this rise. 137 In addition, the coronavirus disease 2019 pandemic affected livelihoods and reduced household incomes, thereby further exposing households to medical impoverishment. 138 The incidence of catastrophic health expenditure we found in sub-Saharan Africa was lower than in China in the last decade, 139 but higher than in Europe, [140][141][142] Asia, 134,143,144 and South America, 145,146 irrespective of the definition used. The incidence may be higher than in Europe and South America because of slow progress in developing a health financing system in sub-Saharan Africa that encourages risk pooling and prepayment contributions and because of continuing overreliance on out-of-pocket payments. 147,148 The high incidence of catastrophic health expenditure we found for specific diseases suggests that health-care costs are driven not just by the cost of treat-ment for acute, life-threatening health shocks, such as emergency surgery or intensive care, but also by the relatively small -but recurrent -cost of chronic illness. We found that about a quarter of households affected by a noncommunicable disease incurred catastrophic health-care costs (when defined as 10% of total household expenditure), a substantially higher figure than for the general population. This result is consistent with growing evidence that noncommunicable disease is a major driver of health-care  137,[149][150][151] In sub-Saharan Africa, the rising burden of noncommunicable diseases has not been matched by measures to curb health-care costs. Policies that simultaneously tackle these diseases and protect households affected by them are urgently needed if the region is to achieve SDG 3.4.1 (i.e. to reduce premature deaths from noncommunicable disease by 25% by 2025) or 1.1.1 (to eradicate extreme poverty). 152 Most sub-Saharan African countries are also burdened by epidemics of infectious diseases, including human immunodeficiency virus/acquired immunodeficiency syndrome (HIV/AIDS), tuberculosis, malaria and pneumonia. 136 We found that the incidence of catastrophic health expenditure was generally higher among households with a patient with HIV/AIDS or tuberculosis than in the rest of the population. This finding suggests that, despite out-of-pocket payment exemptions for people with these conditions, affected households still experience catastrophic health expenditure. The reason could be the high cost of treatment before diagnosis (e.g. from inappropriate care-seeking or irrational drug use), lost income due to prolonged hospitalization, or nonmedical expenditure (e.g. for travel or nutritional supplements). 33, 153 Because the rapid expansion of free antiretroviral therapy and tuberculosis treatment has helped increase life expectancy, financial protection must be extended beyond exemptions for out-of-pocket payments for direct treatment costs.
Our study also showed that the incidence of catastrophic health expenditure was high among people using maternal, neonatal and child health care services. Vulnerable families in most sub-Saharan African countries who require health care for severe obstetric complications, neonatal admission, or paediatric hos-pitalization or surgery are particularly at risk. 154 The sub-Saharan African region alone accounts for two thirds of maternal deaths globally each year. 155 Substantial progress in reducing maternal, neonatal and child mortality is unlikely before countries act to protect households from catastrophic out-of-pocket expenditure when accessing maternal, neonatal and child health-care services. 92,103 The elimination of user fees, for example, could increase access to these services while shielding households from impoverishment. 103 Our study has several strengths. The study is a methodological improvement on previous studies as we used several measures of catastrophic health expenditure. 134,139,143,144 As payment for health care can crowd out both food and nonfood expenditure, it was important to examine health expenditures using the two thresholds of 10% of total household expenditure and 40% of household nonfood expenditure. Also, as we included only population-based studies, our findings are more generalizable to the whole population than those of previous studies.
There are also some limitations. First, survey-based evaluations of catastrophic health expenditure understate the risk faced by poorer households that are unable to seek care because of costs and thus report zero health expenditure. Consequently, our estimates should be taken as lower bounds of the true incidence of catastrophic health expenditure in sub-Saharan Africa. Second, in the absence of a universal definition, we defined catastrophic health expenditure using the thresholds of 10% of total household expenditure and 40% of nonfood expenditure, as did 96% of eligible studies. A different definition could have given different pooled incidences. Finally, information on the UHC service cover-age index was available only for 2015 and 2017 and data on social insurance coverage were sparse, 12,13 which limited confidence in findings related to those two variables.
Despite these limitations, our study provides important evidence for discussions on policy and health financing reform. By demonstrating that a substantial portion of the sub-Saharan African population experience catastrophic costs when accessing health care, our study underscores the urgency of designing effective and inclusive social protection mechanisms. Although identifying interventions was not a study objective, our findings highlight the need for measures such as insurance premium exceptions, co-payment exceptions, free medications and free diagnostic tests for households at most risk. Developing a social insurance system is the preferred long-term solution to catastrophic health expenditure and impoverishment in the region. In the short-term, increased donor funding for both public health care services and country-specific social safety nets are needed to ensure access for poor people. In addition, country-specific, targeted programmes can help reduce health inequity. Regular, nationally representative surveys remain critical tools for tracking health expenditure and for identifying the individuals, households and disease populations most at risk.
The catastrophic health expenses experienced by many people in sub-Saharan Africa threaten poverty alleviation efforts. Stronger financial protection is critically needed in the region if continued progress is to be made towards achieving UHC and meeting the attendant SDGs. ■